1. Field
Embodiments of the present disclosure relate to a measuring device and, in particular, to a measuring device for non-destructive measurement of geometrical parameters of threaded joints. Applications may include, but are not limited to, joints for pipes used in the hydrocarbon industry.
2. Description of the Related Art
In manufacturing processes for threaded objects such as screws, bolts, and threaded pipes, it is beneficial to verify that the geometrical dimensions of the threaded object comply with tolerances set for the object. In addition, information on the nature of the deviation from these tolerances can be used as a feedback to the manufacturing process, thus avoiding rejection of a threaded object later on in the process.
When performing measurement operations for quality control on non-coated threaded objects, difficulties may be encountered. For example, precision and repeatability of measurements are often difficult to achieve. In the past, there have been attempts to improve the accuracy and repeatability of the measurement operations and to make measurement systems capable of measuring the complex thread shape of threaded objects such as the pipes used in the oil industry. In this technical field, a need is felt to measure several parameters, such as taper of the pin and box, thread pitch, thread height, pin or box diameter, pipe ovality, and run in and run out.
In cases where the pipe threading is also coated (e.g. with a dry lubricant), additional difficulties may be encountered. As in the case of non coated pipes, it is beneficial to ensure and verify the geometrical dimensions of the finished piece after the coating process is finished, in order to comply with the tolerances set for the final object.
While ensuring precision and repeatability of measurements remains a difficulty in the case of coated, threaded objects, other problems may also be encountered. For example, when the joints are coated measurement devices are not capable of ensuring that the coating material is not damaged during measurement procedure due to factors such as handling of the pipes and to the use of contact type measuring devices.
Some measuring systems have been proposed for measuring tubular products, with or without coating applied on their surface. However, none of these techniques is especially adapted for measuring threaded joints or, especially the threaded parts of tubular joints that are coated.
In one example, a measurement technique using ultrasound are known, however, this technique has the drawback that it cannot be applied to threaded objects with coatings having small thicknesses. as those applied in threaded joints for the hydrocarbon industry. The wavelength of the ultrasound is much larger than the thicknesses to be measured.
In another example, measurement techniques are known that employ eddy currents. However, this technique has the disadvantage that the measurement device must be placed either in contact or very close to the work piece. It is difficult to use this technique on threaded parts of a joint because of the complex geometry of these parts and because boundary effects are generated when eddy currents are generated on those surfaces. The deformation of the current field lines caused by the geometry, and the fact that the sensor must be very near to the thread surface, are two important constraints that make these devices unsuitable to measurement of pipe threads.
In a further example, measurement techniques are know which are based on X-ray fluorescence or back scattering. In this technique, the coating highlights when it is irradiated and the fluorescence is reabsorbed by the coating. Thus, the amount of fluorescence measured is proportional to the thickness. The results are influenced by several factors. In one aspect, this is not a technique generally applicable. Furthermore, in complex cases, the results depend on the angle of incidence of X-rays. Another drawback of these devices is the fact that the use of X rays is harmful to operators.
Further measurement devices are known that are based on infrared (IR) absorption, where excitation of the coating is made by means of visible light. However, the application of these devices is limited to the cases where the coating is made of material which is excitable by light and on the grade of IR absorption.
Document U.S. Pat. No. 5,712,706 discloses a non-contact laser-based sensor that is guided by a precision mechanical system. The system scans a thread profile and produces a set of computer images of the threading. The computer images are then analyzed to acquire quantitative information about thread characteristics such as pitch, lead, root radius, flank angle, surface roughness, helix variation, and pitch diameter.
However, the device disclosed in U.S. Pat. No. 5,712,706 has the disadvantage that it does not address explicitly the important problem of piece misalignment. Therefore, the system it requires an absolute precision of the operations when aligning the piece to be measured with the mechanical system coordinates. This alignment is conventionally achieved when the piece is at the threading machine.
Unfortunately, performing measurements at the threading machine has several disadvantages. In one aspect, performing measurements at the threading machine adds costly time to the threading manufacturing by preventing inspection and manufacturing processes from running in parallel. In another aspect, performing measurements at the threading machine requires placing delicate optics and precise mechanical components in a hostile environment with cutting oil and strong vibrations present, and to some extent uses the same mechanical movement that has to be verified. Once the pipe has been removed from the lathe, this alignment is very difficult to achieve manually. Consequently, the system disclosed by that document only allows measurement of relative or local magnitudes, such as thread height, by comparing contiguous crests and roots. Errors introduced by a piece misalignment are not “noticed” by that solution and produce an insufficiently precise measurement.
U.S. Pat. No. 5,712,706 also does not address the measurement of important thread parameters. Examples may include, but are not limited to, taper, run-in, run-out, black crest, length of complete thread or specific process parameters such as taper profile, pitch linearity, Fourier mode decomposition of ovality, lathe plate misalignment, hook end angle severity.
The technical article “Lasers gauge pitch” on page 40 of Machine Design, Penton Media, USA, vol. 67, no. 19, 1995 discloses a laser gauge system for gauging threaded sizes.
US Patent Publication No. 2010/0110448 discloses an inspection system for measuring the threaded surface of an internally threaded component. US 2010/0110448 also discloses a method to center the threaded component in the machine. However, this method has limited accuracy and is not compatible with the tolerances to be measured in the field of joints for oil field industry because, due to the weight of the threaded components to be measured, it is not possible to use such system. In particular the process of centring, the drop of a coupling over the collar may cause misalignments that would not be compatible with the tolerances to be measured, which are in the order of microns.
Additionally, both documents disclose devices where sensors are movable along an axis parallel to the axis of the element to be measured. However, they cannot perform measurements along arbitrary trajectories like linear and spiral trajectories.
U.S. Pat. No. 5,521,707 discloses a laser scanner system for rapid precision measurement of thread forms. This system discloses sensors that can perform linear trajectories around the threaded piece to be measured during the rotating movement of said piece. However, such motion is undesirable as such a rotation makes it very difficult to maintain perfect centring between the machine and the threaded piece to be measured.
Another drawback in these documents is that none explicitly addresses the issue of piece misalignment. Therefore, these three systems require a high degree of precision of the when aligning the piece to be measured with the mechanical system coordinates.
Moreover, the measurements obtained with these systems are strongly dependent on the alignment between the element to be measured and the device itself. If the alignment of the element is not substantially perfect, errors may be introduced in the measured values.
In addition, the systems of US Patent Publication No. 2010/0110448A1 and U.S. Pat. No. 5,521,707 can only pair measured values and measuring positions.
Therefore, a need exists for measurement devices and measurement methods for use on threaded joints which provides measurements in a repeatable, satisfactory and sufficiently precise manner.